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equation of line (-1,-1) and (2,5)

can i do it by finding the gradient ( 6) and then doing the y-y1=m(x-x1)? if so what did you get? thank you.
Reply 1
Avatar for 117r
117r
9
Gradient = (change in y)/(change in x) = (5--1)/(2--1) = 2

y-y1=m(x-x1)
y-5 = 2(x-2)
y-5 = 2x-4
y = 2x+1

The gradient isn't 6 mate.
(edited 12 years ago)
Original post by mrdreamerstar

Original post by mrdreamerstar
can i do it by finding the gradient ( 6) and then doing the y-y1=m(x-x1)? if so what did you get? thank you.


The gradient is 2
Gradient = (y2-y1/x2-x1) therefore the gradient = 2 then yes you can use that equation and get Y+1=2(X-1) => Y=2x-3
Reply 4
Avatar for mrdreamerstar
mrdreamerstar
OP
Original post by 117r
Gradient = (5--1)/(2--1) = 2

y-5 = 2(x-2)
y-5 = 2x-4
y = 2x+1

The gradient isn't 6 mate.


oh yeah soz, so 5--1/2--1=6/3=2. okay then what do i do
Reply 5
Avatar for antidotes-
antidotes-
The gradient is equal to: change in y/change in x = 6/3 = 2

Substitute this gradient into the equation y-y1=m(x-x1) with either of the co-ordinates.

For example:
y−5=2(x−2)y-5=2(x-2)
y−5=2x−4y-5=2x-4
y=2x+1y=2x+1

Just to check, I'll try it with the other co-ordinates you have.

y−−1=2(x−−1)y--1=2(x--1)
y+1=2x+2y+1=2x+2
y=2x+1y=2x+1

Therefore, the equation of the line is y=2x+1y=2x+1 or 2x−y+1=02x-y+1=0 depending on how you want to leave it. :smile:
(edited 12 years ago)
Reply 6
Avatar for mrdreamerstar
mrdreamerstar
OP
Original post by mrdreamerstar
oh yeah soz, so 5--1/2--1=6/3=2. okay then what do i do


okay dw i got y=2x+1 aswell. god bless you sir.
Find gradient then find intercept. 6/3=2 gradient is 2 not 6. Y=2x+c. 5=4+=c so equation = y=2x+1 I think.
Reply 8
Avatar for mrdreamerstar
mrdreamerstar
OP
Original post by antidotes-
The gradient is equal to: change in y/change in x = 6/3 = 2

Substitute this gradient into the equation y-y1=m(x-x1) with either of the co-ordinates.

For example:
y-5=2(x-2)
y-5=2x-4
y=2x+1

Just to check, I'll try it with the other co-ordinates you have.

y--1=2(x--1)
y+1=2x+2
y=2x+1

Therefore, the equation of the line is y=2x+1 or 2x-y+1=0 depending on how you want to leave it. :smile:


is 2x+y+1=o in the ax+by+c=0 form?
Reply 9
Avatar for 117r
117r
9
Original post by mrdreamerstar
is 2x+y+1=o in the ax+by+c=0 form?


Yes.

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